1. Technical Field
The present invention relates to computer bus architecture. More specifically, the present invention relates to Inter Integrated Circuit (I2C) buses.
2. Description of Related Art
Many similarities exist between seemingly unrelated designs in consumer, industrial and telecommunication electronics. Examples of similarities include intelligent control, general-purpose circuits (i.e. LCD drivers, I/O ports, RAM) and application-oriented circuits. The Philips Inter Integrated Circuit (I2C) bus is a bi-directional two-wire serial bus designed to exploit these similarities.
Devices on the I2C bus are accessed by individual addresses, 00-FF (even addresses for Writes, odd addresses for reads). The I2C architecture can be used for a variety of functions. One example is Vital Product Data (VPD). Each component in the system contains a small Electrically Erasable Programmable Read Only Memory (EEPROM) (typically 256 bytes) which contains the VPD information such as serial numbers, part numbers, and EC revision level.
I2C busses can connect a number of devices simultaneously to the same pair of bus wires. However, a problem results when one of the devices malfunctions and pulls a bus signal (clock or data) low. The bus will not operate and it is very difficult to determine which of the numerous devices connected to the I2C bus is responsible. A similar problem occurs when one of the bus conductors becomes shorted to a low impedance source, such as, for example, ground.
Therefore, an improved I2C bus from which it is readily determinable the device that has malfunctioned resulting in the bus ceasing to operate would be desirable.
The present invention provides a bus switch module for use in a bus such as an I2C bus. In one embodiment, the switch module includes a control unit and a switch. The control unit includes an input for receiving instructions from a bus driver as to whether to close or open the switch. The switch includes a first and a second data connection which connect the switch to a first and a second segment of the bus and includes a control input for receiving commands from the control unit. The control unit opens and closes the switch in response to instructions received from the bus driver and signals received in the first data connection are passed to the second data connection only when the switch is closed in response to a command from the control unit. Thus, the bus switch module allows a bus driver to isolate devices and switch modules connected in series by opening or closing the switch.